This invention concerns improvements in and relating to valves, more particularly to valves for controlling the flow of any liquid, particularly the flow of water, or other liquids, at pressures in excess of ambient. Valves of the type to which this invention relates are useful for controlling comparatively effortlessly a large pressure drop across the valve when it is closed while at the same time providing a large through flow area to that there is a small loss of pressure when the valve is opened.
Valves are known in which liquid at inlet pressure is admitted to a space behind a diaphragm which acts to close the valve against the action of inlet pressure. Control of such valves is achieved by controlling the bleeding off of liquid under pressure from behind the diaphragm. An example is the U.S. Pat. No. 3,893,475 of July 8, 1975.
A problem arises in relation to such valves which are controlled by a float and are used for example in cattle drinking troughs. Wave action in the water causes the float to bob up and down resulting in the valve intermittently switching on and off, until the trough is eventually overfilled above its correct level, resulting in water wastage in most cases.